JER MET uncertainties and METSignifiance re-estimation

[cmsbuild]

This PR enables the re-computation of the MET significance for the corrected METs on PAT, and enable the JER uncertainty propagation to the MET when the jets are not smeared.

Packages touched:

• PhysicsTools/PatAlgos
• RecoMET/METAlgorithms

Format and content changes :

• JER uncertainties for non-smeared not set to the central value anymore
• central MET significance is not supposed to change when reprocessing AODs (i.e. in slimmedMET)

No real changes of performances/miniAOD size is expected. the MET significance changes only has an effect when the MET is recomputed on top of miniAOD, but the covariance matrix is not recomputed, which means that CPU ressources stays basically the same. The jet smearing used to compute the JER variation is small and does not reduce significantly the processing rate
Automatically ported from CMSSW_8_1_X #16435 (original by @cms-met).

[cmsbuild]

A new Pull Request was created by @cmsbuild for CMSSW_9_0_X.

It involves the following packages:

PhysicsTools/PatAlgos
PhysicsTools/PatUtils
RecoMET/METAlgorithms

@cmsbuild, @cvuosalo, @slava77, @monttj, @davidlange6 can you please review it and eventually sign? Thanks.
@TaiSakuma, @gouskos, @imarches, @ahinzmann, @acaudron, @mmarionncern, @rappoccio, @jdolen, @nhanvtran, @gpetruc, @gkasieczka, @schoef, @ferencek, @mverzett, @mariadalfonso, @pvmulder, @JyothsnaKomaragiri this is something you requested to watch as well.
@slava77, @smuzaffar you are the release manager for this.

cms-bot commands are listed here #13028

[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/16398/console